Saturday, October 29, 2011

How Do Pandas Survive On Bamboo?

The Giant Panda belongs to the order Carnivora, i.e. meat-eating animals. However, 99% of their diet consists of bamboo, and birds, rodents, fish and eggs make up the remaining 1%. Unlike plant-eating animals, carnivores lack the enzymes, bacterias, and the long intestine required to digest fibrous material. Moreover, bamboo has notoriously poor nutritional value.So how do pandas do it?

Researchers have long speculated that panda intestines must have cellulose-munching bacteria that play a role in digestion. But previous attempts to find such bacteria in panda guts had failed. A new study published recently looks at gene sequences in the droppings from seven wild and eight captive giant pandas—a much bigger sample than what was used in previous panda-poop studies

Image: dance4thecure.com

The study leader, Wei and colleagues found that pandas' digestive tracts do in fact contain bacteria similar to those in the intestines of herbivores.
Thirteen of the bacteria species that the team identified are from a family known to break down cellulose, but seven of those species are unique to pandas.

"We think this may be caused by different diet, the unique inner habitat of the gut, or the unique phylogenetic position of their host," Wei said.

Even with help from gut bugs, pandas don't derive much nutrition from bamboo—a panda digests just 17 percent of the 9 to 14 kilograms of dry food it eats each day. Pandas spend up to 16 hours a day eating, and they could ingest up to 8-14 % of their body weight. To put this into perspective, I eat about a kilo of rice everyday (lunch and dinner), and I weight 60 kilograms. Hence I eat about 1.67% of my body weight each day.

Image: ksfm.radio.com

This explains why pandas also evolved a sluggish, energy-conserving lifestyle. In the wild, pandas live in mountainous regions where temperatures could go surprisingly low. Hence it's baffling that pandas could thrive on bamboo alone.

But how and why did pandas became plant-eaters in the first place?

Well, that remains to be seen, though some scientists theorize that, as the ancient human population increased, pandas were pushed into higher altitudes. The animals then adopted a bamboo diet so they wouldn't compete for prey with other meat-eaters, such as Asiatic black bears.

Image: quantum-conservation.org

Not a convincing theory really.

Human population has only increased over the last several thousand years. Prior to that humans were nomadic hunter-gatherers, and civilization has yet to begin. But for pandas to adopt an entirely new diet, or to evolve a digestive system capable of digesting fibrous food, it would require at least several hundred thousand years. Evolution is not an overnight matter. Hence it's unlikely that pandas evolved a vegetarian diet because of humans.
Just my two cents.